Any active domain that is added in a hosting account includes a variety of records that enable it to work properly. In the general case, the name servers (NS records) show where the Internet domain is hosted and they are set on the side of the registrar company, but on the lower level there are certain records created through the hosting company like A (IP address of the website/server), MX (email server), SRV (using a domain for non-website purposes on a specific port number like Voice-over-IP), and many others. With access to these records and by having the capacity to edit them, you could have your web site with company A and your e-mail messages with company B, for example. This gives you more freedom since you can choose the best provider for each of these services and you do not have to stick to a single company. After you pick a hosting company, you have to make sure that you can access all DNS records freely because some companies have an additional fee for this function.